feat(lab2): Threagile threat model + secure variant + auth flow

[SamiKO228]

Goal

This PR submits the threat modeling analysis for Lab 2, covering baseline and secured architectures for the OWASP Juice Shop application along with a custom authentication flow model.

Changes

• Added submission report at submissions/lab2.md
• Added threagile-model-secure.yaml (secured architecture configuration)
• Added threagile-model-auth.yaml (authentication-specific threat model)
• Generated risk analysis artifacts in labs/lab2/output/ and labs/lab2/output-secure/

Testing

• Executed Threagile Docker containers for baseline, secure, and auth-flow models
• Verified risk output generation using jq for severity grouping
• Validated security improvements via manual diff analysis

Artifacts & Screenshots

• Risk reports and generated DFD diagrams are located in the labs/lab2/output/ and labs/lab2/output-secure/ directories.

Checklist

• Title is clear (feat(lab2): threat modeling and hardening analysis)
• No secrets/large temp files committed
• Submission file at submissions/lab2.md exists
• Task 1 — Baseline risk table + top-5 with STRIDE mapping
• Task 2 — Secure variant + risk diff table
• Bonus — Auth-flow model + 3 auth-specific risks